COMP 3000 Essay 1 2010 Question 10 - Revision history

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2010-11-08T15:34:15Z

Unprotected "COMP 3000 Essay 1 2010 Question 10"

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Soma: /* Questions */

2010-10-18T01:44:20Z

Questions

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	=Questions=		=Questions=

	1. Even though flash drives are exponentially faster than traditional HDDs, why are HDDs still the main method of data storage?		#Even though flash drives are exponentially faster than traditional HDDs, why are HDDs still the main method of data storage?
	2. Writing and erasing data are costly operations for a flash based storage drive. Why does modifying data (even a single bit) take the most amount of time?		#Writing and erasing data are costly operations for a flash based storage drive. Why does modifying data (even a single bit) take the most amount of time?
	3. Why is the Flash Translational Layer so important to a flash drive's functionality? Why can you not use the traditional interface to deal with the block layer?		#Why is the Flash Translational Layer so important to a flash drive's functionality? Why can you not use the traditional interface to deal with the block layer?
	4. What particularities/deficiencies of flash memory does any file-system which implements it have to take into account? What are some ways of dealing with them?		#What particularities/deficiencies of flash memory does any file-system which implements it have to take into account? What are some ways of dealing with them?

	=References=		=References=

Soma: Protected "COMP 3000 Essay 1 2010 Question 10" ([edit=sysop] (indefinite) [move=sysop] (indefinite))

2010-10-15T20:03:46Z

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Filitche at 16:49, 15 October 2010

2010-10-15T16:49:43Z

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	Log-based file systems do not share the disadvantages of HDD file systems. Also known as Flash Transitional Layers (FTL), their distinguishing feature is a log that keeps the data which must still be written to disk and then writes it all in one big write. This is useful for flash systems because it allows them to time the expensive write operation in such a way as to not waste resources. It is also useful because, by filling up full blocks at at time, the log-structured file system makes sure that space is used to its fullest capacity. This last fact in turn ensures that it will take the memory a comparatively long time to be filled and that erasures and over-writes will only occur when they absolutely have to. As has been discussed, this is of great benefit to flash memory.		Log-based file systems do not share the disadvantages of HDD file systems. Also known as Flash Transitional Layers (FTL), their distinguishing feature is a log that keeps the data which must still be written to disk and then writes it all in one big write. This is useful for flash systems because it allows them to time the expensive write operation in such a way as to not waste resources. It is also useful because, by filling up full blocks at at time, the log-structured file system makes sure that space is used to its fullest capacity. This last fact in turn ensures that it will take the memory a comparatively long time to be filled and that erasures and over-writes will only occur when they absolutely have to. As has been discussed, this is of great benefit to flash memory.

	A log structured file system also has advantages when it comes to wear leveling. These are made actual through various technological innovations which include a translation table and banks. The translation table is a structure which maps each block of memory to a flag which keeps track of its state. When a block is being written to, the FTL marks its state as "allocated" so as to prevent other write-processes from ~~targeting~~ the same block. The FTL then goes on to write the data in the allocated blocks. After this is finished, the relevant block's state becomes "pre-valid" If writing to this block involved the erasure from another block, the now old block is at marked as invalid (ready for erasure) and the ~~new block is finally marked as valid after that.[8]~~		A log structured file system also has advantages when it comes to wear leveling. These advantages mostly come from the use of banks and the garbage collector. A bank is essentially a group of sequential addresses which keeps track of when it was last updated using timestamps.When the FTL receives a request to write something to memory, it uses a list of these to determine which area of the drive should be used (ie. which one has the fewest timestamps). Then, it only writes to that bank, until it is full before switching to another. Very importantly, the system also keeps a Cleaning Bank list which indicates which banks need to be emptied out. This feature makes certain that writes and erasures are never mixed in the same bank and is also integral to the whole erasure process, which is in turn one of the key feature of the log-based file system. [8]

	~~On another technical level, the FTL also works with banks~~. A bank is essentially a group of sequential addresses which keeps track of when it was last updated using timestamps.When the FTL receives a request to write something to memory, it uses a list of these to determine which area of the drive should be used. Then, it only writes to that bank, until it is full before switching to another. Very importantly, the system also keeps a Cleaning Bank list which indicates which banks need to be emptied out. This feature makes certain that writes and erasures are never mixed in the same bank and is also integral to the whole erasure process, which is in turn one of the key feature of the log-based file system. [8]

	At the heart of this process is the garbage collector: When the FTL realizes that there is not enough room to write new data onto the drive, it runs a garbage collection routine. This routine selects a segment to be cleaned, copies all of the valid data into a new segment, then erases everything in the old segment. This frees up the otherwise useless invalidated blocks. Furthermore, because the collector does not erase every block the moment it becomes invalidated but ony does it by the bank, time is saved when the expensive erase operation is called. Due to the slowness of the erasures, the kernel typically conducts the cleaning when the drive is idle and many resources are available for this process. [SOURCE]		At the heart of this process is the garbage collector: When the FTL realizes that there is not enough room to write new data onto the drive, it runs a garbage collection routine. This routine selects a segment to be cleaned, copies all of the valid data into a new segment, then erases everything in the old segment. This frees up the otherwise useless invalidated blocks. Furthermore, because the collector does not erase every block the moment it becomes invalidated but ony does it by the bank, time is saved when the expensive erase operation is called. Due to the slowness of the erasures, the kernel typically conducts the cleaning when the drive is idle and many resources are available for this process. [SOURCE]

			Thus, the advantages of the log-based file system arise from its log-structure but also have to do with wear leveling and the optimization of writes and erasures on the block level. These advantages are made actual through the log itself, the use of banks and through the garbage collector.
	Thus, the advantages of the log-based file system arise from its log-structure but also have to do with wear leveling and the optimization of writes and erasures on the block level. ~~The former is accomplished by means of~~ the log itself ~~and its intelligent~~ use ~~when it comes to deciding where to write. The latter, through certain technical tools such as allocation-technology,~~ banks and~~, of course,~~ the garbage collector.

	==Conclusion==		==Conclusion==

	In this way, thanks to its wear-leveling~~, banks and garbage collector~~, the log-based file-system is far better suited to working with flash memory than a traditional HDD file system. The latter is utterly unfit for this task due to its placing primacy on the minimization of seeks rather than on the minimization and management of erasures. Dealing smartly with erasures is extremely important for a flash memory file system, as that memory type's particular weaknesses, the limited number of erasure cycles, the necessity to erase by the block and the relative slowness of the erasures themselves, all have to do with erasing. A good flash memory file system must therefore be built with the aim of making the best of these weaknesses and this is precisely the reason why older disk-based file systems are not suitable for flash memory while log-based file systems are.		In this way, thanks to its special wear-leveling features, the log-based file-system is far better suited to working with flash memory than a traditional HDD file system. The latter is utterly unfit for this task due to its placing primacy on the minimization of seeks rather than on the minimization and management of erasures. Dealing smartly with erasures is extremely important for a flash memory file system, as that memory type's particular weaknesses, the limited number of erasure cycles, the necessity to erase by the block and the relative slowness of the erasures themselves, all have to do with erasing. A good flash memory file system must therefore be built with the aim of making the best of these weaknesses and this is precisely the reason why older disk-based file systems are not suitable for flash memory while log-based file systems are.

	=Questions=		=Questions=

Filitche at 16:38, 15 October 2010

2010-10-15T16:38:29Z

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	Log-based file systems do not share the disadvantages of HDD file systems. Also known as Flash Transitional Layers (FTL), their distinguishing feature is a log that keeps the data which must still be written to disk and then writes it all in one big write. This is useful for flash systems because it allows them to time the expensive write operation in such a way as to not waste resources. It is also useful because, by filling up full blocks at at time, the log-structured file system makes sure that space is used to its fullest capacity. This last fact in turn ensures that it will take the memory a comparatively long time to be filled and that erasures and over-writes will only occur when they absolutely have to. As has been discussed, this is of great benefit to flash memory.		Log-based file systems do not share the disadvantages of HDD file systems. Also known as Flash Transitional Layers (FTL), their distinguishing feature is a log that keeps the data which must still be written to disk and then writes it all in one big write. This is useful for flash systems because it allows them to time the expensive write operation in such a way as to not waste resources. It is also useful because, by filling up full blocks at at time, the log-structured file system makes sure that space is used to its fullest capacity. This last fact in turn ensures that it will take the memory a comparatively long time to be filled and that erasures and over-writes will only occur when they absolutely have to. As has been discussed, this is of great benefit to flash memory.

	A log structured file system also has advantages when it comes to wear leveling. These are made actual through various technological innovations which include a translation table and banks. The translation table is a structure which maps each block of memory to a flag which keeps track of its state. ~~These states are~~ "allocated",		A log structured file system also has advantages when it comes to wear leveling. These are made actual through various technological innovations which include a translation table and banks. The translation table is a structure which maps each block of memory to a flag which keeps track of its state. When a block is being written to, the FTL marks its state as "allocated" so as to prevent other write-processes from targeting the same block. The FTL then goes on to write the data in the allocated blocks. After this is finished, the relevant block's state becomes "pre-valid" If writing to this block involved the erasure from another block, the now old block is at marked as invalid (ready for erasure) and the new block is finally marked as valid after that.[8]

			On another technical level, the FTL also works with banks. A bank is essentially a group of sequential addresses which keeps track of when it was last updated using timestamps.When the FTL receives a request to write something to memory, it uses a list of these to determine which area of the drive should be used. Then, it only writes to that bank, until it is full before switching to another. Very importantly, the system also keeps a Cleaning Bank list which indicates which banks need to be emptied out. This feature makes certain that writes and erasures are never mixed in the same bank and is also integral to the whole erasure process, which is in turn one of the key feature of the log-based file system. [8]
	When a block is being written to, the FTL marks the blocks needed as "allocated". This prevents other data from being written to the block that has already been allocated. The FTL then goes on to write the data in the allocated blocks. After this is finished, the relevant block's state becmes "pre-valid". Next, the block is marked as valid.On another technical level, the FTL also works with banks. A bank is essentially a group of sequential addresses which keeps track of when it was last updated using timestamps.When the FTL receives a request to write something to memory, it uses a list of these to determine which area of the drive should be used. Then, it only writes to that bank, until it is full before switching to another. Very importantly, the system also keeps a Cleaning Bank list which indicates which banks need to be emptied out. This feature makes certain that writes and erasures are never mixed in the same bank and is also integral to the whole erasure process, which is in turn one of the key feature of the log-based file system. [8]

	At the heart of this process is the garbage collector: When the FTL realizes that there is not enough room to write new data onto the drive, it runs a garbage collection routine. This routine selects a segment to be cleaned, copies all of the valid data into a new segment, then erases everything in the old segment. This frees up the otherwise useless invalidated blocks. Furthermore, because the collector does not erase every block the moment it becomes invalidated but ony does it by the bank, time is saved when the expensive erase operation is called. Due to the slowness of the erasures, the kernel typically conducts the cleaning when the drive is idle and many resources are available for this process. [SOURCE]		At the heart of this process is the garbage collector: When the FTL realizes that there is not enough room to write new data onto the drive, it runs a garbage collection routine. This routine selects a segment to be cleaned, copies all of the valid data into a new segment, then erases everything in the old segment. This frees up the otherwise useless invalidated blocks. Furthermore, because the collector does not erase every block the moment it becomes invalidated but ony does it by the bank, time is saved when the expensive erase operation is called. Due to the slowness of the erasures, the kernel typically conducts the cleaning when the drive is idle and many resources are available for this process. [SOURCE]

Filitche at 16:20, 15 October 2010

2010-10-15T16:20:04Z

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	Log-based file systems do not share the disadvantages of HDD file systems. Also known as Flash Transitional Layers (FTL), their distinguishing feature is a log that keeps the data which must still be written to disk and then writes it all in one big write. This is useful for flash systems because it allows them to time the expensive write operation in such a way as to not waste resources. It is also useful because, by filling up full blocks at at time, the log-structured file system makes sure that space is used to its fullest capacity. This last fact in turn ensures that it will take the memory a comparatively long time to be filled and that erasures and over-writes will only occur when they absolutely have to. As has been discussed, this is of great benefit to flash memory.		Log-based file systems do not share the disadvantages of HDD file systems. Also known as Flash Transitional Layers (FTL), their distinguishing feature is a log that keeps the data which must still be written to disk and then writes it all in one big write. This is useful for flash systems because it allows them to time the expensive write operation in such a way as to not waste resources. It is also useful because, by filling up full blocks at at time, the log-structured file system makes sure that space is used to its fullest capacity. This last fact in turn ensures that it will take the memory a comparatively long time to be filled and that erasures and over-writes will only occur when they absolutely have to. As has been discussed, this is of great benefit to flash memory.

	A log structured file system also has advantages when it comes to wear leveling. These are made actual through ~~var~~		A log structured file system also has advantages when it comes to wear leveling. These are made actual through various technological innovations which include a translation table and banks. The translation table is a structure which maps each block of memory to a flag which keeps track of its state. These states are "allocated",

	The FTL is what makes it possible to combine the above features with a more traditional memory-management structure. It has a translation table, where each physical memory address is associated with an emulated block sectors. This allows a traditional file system that uses block sectors to be used on the flash drive. The FTL is able to achieve this by giving each block a flag which keeps track of its state. When blocks are being written to, the FTL marks them as allocated.

	When a block is being written to, the FTL marks the blocks needed as "allocated". This prevents other data from being written to the block that has already been allocated. The FTL then goes on to write the data in the allocated blocks. After this is finished, the relevant block's state becmes "pre-valid". Next, the block is marked as valid.On another technical level, the FTL also works with banks. A bank is essentially a group of sequential addresses which keeps track of when it was last updated using timestamps.When the FTL receives a request to write something to memory, it uses a list of these to determine which area of the drive should be used. Then, it only writes to that bank, until it is full before switching to another. Very importantly, the system also keeps a Cleaning Bank list which indicates which banks need to be emptied out. This feature makes certain that writes and erasures are never mixed in the same bank and is also integral to the whole erasure process, which is in turn one of the key feature of the log-based file system. [8]		When a block is being written to, the FTL marks the blocks needed as "allocated". This prevents other data from being written to the block that has already been allocated. The FTL then goes on to write the data in the allocated blocks. After this is finished, the relevant block's state becmes "pre-valid". Next, the block is marked as valid.On another technical level, the FTL also works with banks. A bank is essentially a group of sequential addresses which keeps track of when it was last updated using timestamps.When the FTL receives a request to write something to memory, it uses a list of these to determine which area of the drive should be used. Then, it only writes to that bank, until it is full before switching to another. Very importantly, the system also keeps a Cleaning Bank list which indicates which banks need to be emptied out. This feature makes certain that writes and erasures are never mixed in the same bank and is also integral to the whole erasure process, which is in turn one of the key feature of the log-based file system. [8]

Filitche at 16:15, 15 October 2010

2010-10-15T16:15:22Z

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	==Traditionally Optimized File Systems==		==Traditionally Optimized File Systems==

	~~Since the kernel asks for a block number, a conventional hard disk drive (~~HDD) file-system is not optimized to work with flash memory. The reason for this is that conventional hard-disks have different constraints from those of flash memory - their primary problem is to reduce seeking time, while the primary problem when working with flash memory is to erase in a minimal and balanced way.		An HDD file-system, however, is not optimized to work with flash memory. The reason for this is that conventional hard-disks have different constraints from those of flash memory - their primary problem is to reduce seeking time, while the primary problem when working with flash memory is to erase in a minimal and balanced way.

	The most consuming process for an HDD is seeking data by relocating the read-head and spinning the magnetic disk. A traditional file system optimizes the way it stores data by placing related blocks close-by on the disk in order to minimize mechanical movement within the HDD. One of the great advantages of flash memory, which accounts for its fast read speed, is that there is no need to seek data physically. This is also why defragmentaion, a procedure used by HDDs to put files into more convenient configurations and thus minimize seeking times, loses its purpose in a flash memory context. Indeed, the unnecessary erasures that it entails are both inefficient and harmful for a flash memory unit.		The most consuming process for an HDD is seeking data by relocating the read-head and spinning the magnetic disk. A traditional file system optimizes the way it stores data by placing related blocks close-by on the disk in order to minimize mechanical movement within the HDD. One of the great advantages of flash memory, which accounts for its fast read speed, is that there is no need to seek data physically. This is also why defragmentaion, a procedure used by HDDs to put files into more convenient configurations and thus minimize seeking times, loses its purpose in a flash memory context. Indeed, the unnecessary erasures that it entails are both inefficient and harmful for a flash memory unit. [SOURCE?]

	This comes directly out of flash memory's aforementioned constraints: the slow block-sized erasures and the limited number of erase-cycles. Because of these, a flash optimal file system needs to minimize its erase operations and also to spread out its erasures in such a way as to avoid the formation of hot-spots: sections of memory which have undergone a disproportionately high number of erasures and are thus in danger of burning out. This process of spreading out data is referred to as ''wear leveling''. To minimize hot-spots, a system using flash memory would have to write new data to empty memory blocks. This method would also call for some sort of garbage collection to conduct necessary erasure operations while the system is idle~~. It makes better sense to do these at this time because of the slow nature of erasures in the flash memory context~~. Of course, there is no such feature in a traditional HDD file-system. For the reasons given above, HDD systems are unsuitable for use with flash memory.		This comes directly out of flash memory's aforementioned constraints: the slow block-sized erasures and the limited number of erase-cycles. Because of these, a flash optimal file system needs to minimize its erase operations and also to spread out its erasures in such a way as to avoid the formation of hot-spots: sections of memory which have undergone a disproportionately high number of erasures and are thus in danger of burning out. This process of spreading out data is referred to as ''wear leveling''. To minimize hot-spots, a system using flash memory would have to write new data to empty memory blocks. [3] This method would also call for some sort of garbage collection to conduct necessary erasure operations while the system is idle. Of course, there is no such feature in a traditional HDD file-system. For the reasons given above, HDD systems are unsuitable for use with flash memory.

	==Flash Optimized File Systems==		==Flash Optimized File Systems==

	Log-based file systems~~, however,~~ do not share the disadvantages of HDD file systems. Also known as Flash Transitional Layers (FTL), their distinguishing feature is a log that keeps the data which must still be written to disk and then writes it all in one big write. This is useful for flash systems because it allows them to time the expensive write operation in such a way as to not waste resources ~~and~~ also because, by filling up full blocks at at time, the log-structured file system makes sure that space is used to its fullest capacity. This last fact in turn ensures that it will take the memory a comparatively long time to be filled and that erasures and over-writes will only occur when they absolutely have to. As has been discussed, this is of great benefit to flash memory.		Log-based file systems do not share the disadvantages of HDD file systems. Also known as Flash Transitional Layers (FTL), their distinguishing feature is a log that keeps the data which must still be written to disk and then writes it all in one big write. This is useful for flash systems because it allows them to time the expensive write operation in such a way as to not waste resources. It is also useful because, by filling up full blocks at at time, the log-structured file system makes sure that space is used to its fullest capacity. This last fact in turn ensures that it will take the memory a comparatively long time to be filled and that erasures and over-writes will only occur when they absolutely have to. As has been discussed, this is of great benefit to flash memory.

	A log structured file system also ~~keeps a log of how many times each block of data~~ has ~~been erased and this is good for conducting~~ wear leveling - a process the purpose of which is to prevent particular blocks from being erased more than others. As already discussed, the purpose of such a practice is to reduce hot-spots. Wear-leveling writes data that does not change to blocks that have been erased frequently thus decreasing the probability that those blocks will be erased even more. Similarly, it tries to write evenly to all the blocks so as to maximize the hard-drive's overall lifespan. ~~[3]~~		A log structured file system also has advantages when it comes to wear leveling. These are made actual through var

	The FTL is what makes it possible to combine the above features with a more traditional memory-management structure. It has a translation table, where each physical memory address is associated with an emulated block sectors. This allows a traditional file system that uses block sectors to be used on the flash drive. The FTL is able to achieve this by giving each block a flag which keeps track of its state. When blocks are being written to, the FTL marks them as allocated.		The FTL is what makes it possible to combine the above features with a more traditional memory-management structure. It has a translation table, where each physical memory address is associated with an emulated block sectors. This allows a traditional file system that uses block sectors to be used on the flash drive. The FTL is able to achieve this by giving each block a flag which keeps track of its state. When blocks are being written to, the FTL marks them as allocated.

Filitche at 16:05, 15 October 2010

2010-10-15T16:05:38Z

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	=Answer=		=Answer=

	First introduced in the late 80s, Flash-memory is a light, energy-independent, compact, shock-resistant and efficiently readable type of storage. Because of the particular limitations of this kind of memory, flash file systems require a fundamentally different system architecture than disk-based file-systems. The particular limitations that lead to this necessity are flash-memory’s limited number of erase-cycles, the slowness of its writes and erasures, as well as its need to conduct erasures one entire block at a time. A typical disk-based file-system is not suitable for working with flash ~~memory~~ as it erases far too frequently and indiscriminately while being simultaneously optimized for other constraints that do not affect flash memory. This means that a different solution is necessary and that solution is the log-based file-system which is far better suited to working with flash ~~memory~~ because it is able to optimize a flash unit's lifespan through the log-structure of writes and wear-leveling, as well as its efficiency through the better management of writes and erasures.		First introduced in the late 80s, Flash-memory is a light, energy-independent, compact, shock-resistant and efficiently readable type of storage. Because of the particular limitations of this kind of memory, flash file systems require a fundamentally different system architecture than disk-based file-systems. The particular limitations that lead to this necessity are flash-memory’s limited number of erase-cycles, the slowness of its writes and erasures, as well as its need to conduct erasures one entire block at a time. A typical disk-based file-system is not suitable for working with flash as it erases far too frequently and indiscriminately while being simultaneously optimized for other constraints that do not affect flash memory. This means that a different solution is necessary and that solution is the log-based file-system which is far better suited to working with flash because it is able to optimize a flash unit's lifespan through the log-structure of writes and wear-leveling, as well as its efficiency through the better management of writes and erasures.

	==Flash Memory==		==Flash Memory==

	Though Flash memory has many advantages it also has several ~~key~~ disadvantages which are of key relevance for anyone attempting to implement an file system to work with it.		Though Flash memory has many advantages it also has several disadvantages which are of key relevance for anyone attempting to implement an file system to work with it.

	~~There are two basic forms of~~ the ~~flash storage system~~, ~~NOR~~ and ~~NAND. Each type~~ has its advantages and disadvantages. NOR has the ~~fastest~~ read times, but is much slower at writing. NAND on the other hand has much more capacity, faster write times, is less expensive, and ~~has a much~~ longer ~~life expectancy~~. This means that NAND is the superior form of flash for long term storage, while NOR is preferred for computer embedded read-only functions. [2]		Though flash memory on the whole has strengths and weaknesses, it is also divided into two sub-types and each of these also has its own advantages and disadvantages that shall be briefly examined here. The two types of flash memory are NOR and NAND: NOR has the faster read times, but is much slower at writing. NAND on the other hand has much more capacity, faster write times, is less expensive, and can last about ten times longer. This means that NAND is the superior form of flash for long term storage, while NOR is preferred for computer embedded read-only functions. [2] Although these two types of flash are different, they are not sufficiently so as to merit an independence file system approach for each one. Thus, we shall not differentiate between them for the rest of this article.

	~~More and more people~~ use flash ~~memory~~, ~~with many sizes~~ of ~~drives~~, ~~ranging from~~ a ~~few hundred megabyte USB key, to a few terabyte internal solid-state drive(SSD). Two main reasons for this movement are because~~ of flash's extremely fast read times, ~~and its falling price. A typical flash drive has~~ read ~~speeds~~ of ~~up to 14~~ times ~~faster than a~~ hard disk ~~drive (HDD)~~.[17]		The use of flash has grown dramatically in recent years, primarily for the purpose of portable devices and portable data storage. While this phenomenon has been partially due to the falling price of the product, it has been more of a result of flash's strengths - these make it a near optimal solution for the many portable devices which are currently in vogue. These strengths, besides compactness, resistance to shock and independence from power-supplies also include extremely fast read times. Indeed, the read times of flash devices can be as much as fourteen times those of hard disk drives. [17]

	~~The extreme read speed makes flash drives a preferred method of storing games. This effectively makes loading times virtually non-existent. There is~~ however ~~a downside to this method. Games constantly save~~, ~~modify, and change files wearing out~~ the ~~blocks much quicker. Flash drives have been shown to be effective~~ for ~~the use in web-servers for running their CSS scripts or HTML pages.~~		Despite these advantages, however, are not the preferred storage method for home PCs. The reason for this is not just that other kinds of memory are still significantly cheaper, but also that flash memory has certain limitations built into it. The most critical of these is that each block of flash memory can only be erased approximately 100,000 times (or just 10000 if its NOR flash).[14] This poses a problem because of flash memory's second significant drawback: when modifying a file, even if its a single bit, the entire block must be erased, and rewritten. This erase/rewrite slows down the write operation considerably, making it actually slower to write or erase a file on flash than to a hard disk drive (HDD).[8]

	~~Although flash drives offer exponentially faster read-speeds than HDDs, they still have not become the main source of data management~~. The reason for this is ~~because HDDs~~ are ~~simply much~~ cheaper, ~~and~~ flash ~~drives still have many faults~~. The most critical ~~fault~~ is that each block in flash memory can only be erased approximately 100,000 times (or just 10000 if its NOR flash).[14] This poses a problem because of flash memory's second significant drawback: when modifying a file, even if its a single bit, the entire block must be erased, and rewritten. This erase/rewrite slows down the write operation considerably, making it actually slower to write a file to flash than an HDD.[8]

	Thus, though flash does offer much faster read-times, it comes with the heavy constraints on a limited number of erase cycles, slow write and erase times and the necessity to be erased a block at a time.		Thus, though flash does offer much faster read-times, it comes with the heavy constraints on a limited number of erase cycles, slow write and erase times and the necessity to be erased a block at a time.

Filitche at 14:19, 15 October 2010

2010-10-15T14:19:08Z

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	==Flash Memory==		==Flash Memory==

	Though Flash memory has many advantages it also has several key disadvantages which are of key relevance for anyone attempting to ~~impliment~~ an file system to work with it.		Though Flash memory has many advantages it also has several key disadvantages which are of key relevance for anyone attempting to implement an file system to work with it.

	There are two basic forms of the flash storage system, NOR and NAND. Each type has its advantages and disadvantages. NOR has the fastest read times, but is much slower at writing. NAND on the other hand has much more capacity, faster write times, is less expensive, and has a much longer life expectancy. This means that NAND is the superior form of flash for long term storage, while NOR is preferred for computer embedded read-only functions. [2]		There are two basic forms of the flash storage system, NOR and NAND. Each type has its advantages and disadvantages. NOR has the fastest read times, but is much slower at writing. NAND on the other hand has much more capacity, faster write times, is less expensive, and has a much longer life expectancy. This means that NAND is the superior form of flash for long term storage, while NOR is preferred for computer embedded read-only functions. [2]
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	The most consuming process for an HDD is seeking data by relocating the read-head and spinning the magnetic disk. A traditional file system optimizes the way it stores data by placing related blocks close-by on the disk in order to minimize mechanical movement within the HDD. One of the great advantages of flash memory, which accounts for its fast read speed, is that there is no need to seek data physically. This is also why defragmentaion, a procedure used by HDDs to put files into more convenient configurations and thus minimize seeking times, loses its purpose in a flash memory context. Indeed, the unnecessary erasures that it entails are both inefficient and harmful for a flash memory unit.		The most consuming process for an HDD is seeking data by relocating the read-head and spinning the magnetic disk. A traditional file system optimizes the way it stores data by placing related blocks close-by on the disk in order to minimize mechanical movement within the HDD. One of the great advantages of flash memory, which accounts for its fast read speed, is that there is no need to seek data physically. This is also why defragmentaion, a procedure used by HDDs to put files into more convenient configurations and thus minimize seeking times, loses its purpose in a flash memory context. Indeed, the unnecessary erasures that it entails are both inefficient and harmful for a flash memory unit.

	This comes directly out of flash memory's aforementioned constraints: the slow block-sized erasures and the limited number of erase-cycles. Because of these, a flash optimal file system needs to minimize its erase operations and also to spread out its erasures in such a way as to avoid the formation of hot-spots: sections of memory which have undergone a disproportionately high number of erasures and are thus in danger of burning out. This process of spreading out data is referred to as ''wear leveling''. To minimize ~~hotspots~~, a system using flash memory would have to write new data to empty memory blocks. This method would also call for some sort of garbage collection to conduct necessary erasure operations while the system is idle. It makes better sense to do these at this time because of the slow nature of erasures in the flash memory context. Of course, there is no such feature in a traditional HDD file-system. For the reasons given above, HDD systems are unsuitable for use with flash memory.		This comes directly out of flash memory's aforementioned constraints: the slow block-sized erasures and the limited number of erase-cycles. Because of these, a flash optimal file system needs to minimize its erase operations and also to spread out its erasures in such a way as to avoid the formation of hot-spots: sections of memory which have undergone a disproportionately high number of erasures and are thus in danger of burning out. This process of spreading out data is referred to as ''wear leveling''. To minimize hot-spots, a system using flash memory would have to write new data to empty memory blocks. This method would also call for some sort of garbage collection to conduct necessary erasure operations while the system is idle. It makes better sense to do these at this time because of the slow nature of erasures in the flash memory context. Of course, there is no such feature in a traditional HDD file-system. For the reasons given above, HDD systems are unsuitable for use with flash memory.

	==Flash Optimized File Systems==		==Flash Optimized File Systems==

Filitche at 14:18, 15 October 2010

2010-10-15T14:18:38Z

← Older revision		Revision as of 14:18, 15 October 2010
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	Though Flash memory has many advantages it also has several key disadvantages which are of key relevance for anyone attempting to impliment an file system to work with it.		Though Flash memory has many advantages it also has several key disadvantages which are of key relevance for anyone attempting to impliment an file system to work with it.

	~~Originally conceived as an improved alternative to EPROMs[7], Flash memory is non-volatile(power-supply independent) storage space that has become more popular recently due to its fast fetch times.~~ There are two basic forms of the flash storage system, NOR and NAND. Each type has its advantages and disadvantages. NOR has the fastest read times, but is much slower at writing. NAND on the other hand has much more capacity, faster write times, is less expensive, and has a much longer life expectancy. This means that NAND is the superior form of flash for long term storage, while NOR is preferred for computer embedded read-only functions. [2]		There are two basic forms of the flash storage system, NOR and NAND. Each type has its advantages and disadvantages. NOR has the fastest read times, but is much slower at writing. NAND on the other hand has much more capacity, faster write times, is less expensive, and has a much longer life expectancy. This means that NAND is the superior form of flash for long term storage, while NOR is preferred for computer embedded read-only functions. [2]

	More and more people use flash memory, with many sizes of drives, ranging from a few hundred megabyte USB key, to a few terabyte internal solid-state drive(SSD). Two main reasons for this movement are because of flash's extremely fast read times, and its falling price. A typical flash drive has read speeds of up to 14 times faster than a hard disk drive (HDD).[17]		More and more people use flash memory, with many sizes of drives, ranging from a few hundred megabyte USB key, to a few terabyte internal solid-state drive(SSD). Two main reasons for this movement are because of flash's extremely fast read times, and its falling price. A typical flash drive has read speeds of up to 14 times faster than a hard disk drive (HDD).[17]